Erosion resistant soft seated valve trim

ABSTRACT

The disclosure is related to a high pressure fluid control valve including a valve seat made from a resilient, deformable material and a main valve plug which is matable with the resilient, deformable valve seat. A selectively, axially displaceable valve stem is associated with the valve plug whereby a contact load placed upon the valve plug by the valve stem will cause the valve plug to be become imbedded within the deformable material comprising the valve seat when the valve is closed and thereby conform the deformable seat precisely to the contour and configuration of those portions of the valve plug which mate with the valve seat. In this manner, a precise zero-leakage mating is obtained each and every time the plug is mated with the seat. In accordance with the invention, an auxiliary throttle plug is associated with the main valve plug and is arranged to mate with a second, metal valve seat which is arranged in an area removed from the resilient, deformable valve seat. The axial movements of each of the valve plug and the throttle plug are coordinated in a manner whereby the primary throttling areas for the fluid flow, particularly during valve opening and valve closing operations are displaced to portions of the valve structure which are remote from the resilient, deformable valve seat.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention is directed to a high pressure control valve andin particular to a new and improved soft seat design.

One of the principal functions of a high pressure control valve is toprovide a complete and leak-proof shut off of fluid flow when the valveis in the closed position. Typically, this is accomplished by mating anaxially movable valve plug with a stationary valve seat, whereby thevalve plug and seat isolate the high pressure fluid from the fluidoutlet portions of the control valve. In most conventional valvedesigns, the valve seat is made from metal to provide a so-called"hard-seat" arrangement. The valve plug is also made from metal andtherefore the fluid flow shut off is achieved by a metal-to-metalcontact between the valve plug and the valve seat. In such a hard-seatarrangement, it is critical that the valve plug and seat precisely matewith one another to completely shut off and isolate the high pressurefluid from the valve outlet. The manufacture of each of the valve plugand seat from metal is advantageous in a high pressure application inthat the metal components are fairly resistant to the deleteriouseffects of the high pressure fluid flow including cavitation and othereroding effects caused by the high pressure fluid flow and the generallyhigh pressure drops experienced by the fluid flow as it passes throughthe valve structure. Nevertheless, it is widely recognized in the valveindustry that it is virtually impossible to obtain a zero-leakage matingbetween the valve plug and seat when utilizing a hard metal-to-metalcontact arrangement.

Moreover, in time, the high pressure fluid flow through the valve causeswear and tear on the metal components. In addition, impurities foundwithin the fluid flow may become trapped between the valve plug andvalve seat during valve shut off to thereby pit and otherwise damage thevalve plug and/or valve seat. It should be understood that the normalwear and tear and possible damage to the valve components caused byimpurities found within the fluid flow will not occur uniformlythroughout the mating portions of the metal valve plug and metal seat.Thus, in time, the mating relationship between the valve plug and seatwill become less precise resulting in a greater amount of fluid leakagewhen the valve is in the shut off position. Accordingly, the valve willgradually become less effective as a means to completely interrupt fluidflow. In certain severe duty valve applications, such as pumprecirculation, complete fluid isolation is critical and the gradual anduneven erosion of the metal components of the valve make such hard seatdesigns somewhat less than desirable in the critical, severe dutyapplications.

In order to overcome the shortcomings of the hard-seat design, thoseskilled in the art have proposed the use of a so-called "soft seat"design. In such a valve arrangement, the seat is made from a resilient,deformable material, whereby the contact load placed upon the valve plugwill cause the valve plug to become imbedded within the soft seat andthereby conform the soft, deformable seat precisely to the contour andconfiguration of the valve plug mating portions. In this manner, thesoft seat provides a precise mating each and every time the plug ismated with the seat. Moreover, the high degree of seat conformanceachieved with a soft seat design is obtainable with stem forces that arefar lower than the stem forces required to achieve a good leak-tightshut off in a metal-to-metal arrangement. Accordingly, a zero leakagevalve shut off may be obtained far more readily and easily in a softseat design than in a hard seat design. However, a problem associatedwith the soft seat arrangement is the rather rapid erosion of theresilient deformable material utilized to manufacture the soft seat.Typically, as the valve plug is lifted from the valve seat, a very highpressure fluid flow is immediately throttled directly over the valveseat as fluid flow is permitted to resume between the valve plug and thevalve seat. It is this throttling effect which generally erodes the softseat valve material. As a consequence of the relatively rapid wear downof the soft valve seat, such soft seat valves require a more thandesirable amount of down time in order to rebuild or replace the softseat. Indeed, the rapid erosion may preclude the use of a soft seat incertain high pressure applications.

It is a primary objective of the present invention to provide a softseat valve with additional novel means to displace the deleteriousthrottling effects of the fluid flow away from the soft valve seat.Generally, the invention comprises a high pressure control valveincluding a soft seat made from a resilient, deformable material. Inaccordance with a significant feature of the invention, the controlvalve is provided with a main valve plug which is matable with the softseat and an additional, auxiliary throttle plug which is coaxial withand axially movable relative to the main valve plug. The throttle plugis arranged to mate with a second metal valve seat which is concentricwith and arranged in an area removed from the soft valve seat. Inaccordance with the invention, the axial movements of each of the mainvalve plug and the throttle plug are coordinated in a manner whereby theprimary throttling areas for the fluid flow are displaced to portions ofthe valve structure which are remote from the soft seat, as will appear.

As contemplated by the preferred embodiment of the invention, the mainplug comprises a generally cylindrical, at least partially hollow plughaving a valve seat-engaging rim which circumscribes the at leastpartially hollow portion of the plug. The throttle plug is axiallyreceived within the hollow portion of the main plug and is associatedwith a throttle plug retaining means arranged to retain the throttleplug within the main plug hollow portion while accommodating a limited,axial movement of the throttle plug relative to the main plug. Moreover,a biasing means urges the throttle plug away from the main plug wherebyone end of the throttle plug ordinarily protrudes from the hollowportion of the main plug beyond the valve seat-engaging rim. When in theclosed position, the rim of the main plug contacts the soft seat underpressure from a valve stem to form a leak-tight, fully conformed matingbetween the rim and the deformable, resilient seat. In this manner, ahighly effective fluid flow shut off is achieved. In addition, theprotruding end of the throttle plug will be in a mating relation withthe second, metal valve seat.

Pursuant to the invention, the valve is operated such that during theinitial opening of the valve, the rim of the main plug is displaced fromthe soft seat while unbalanced pressure effects, as will be more fullydescribed below, and the biasing means act to retain the throttle plugin contact with the second, metal seat. At this point, the only fluidflow will be leakage through the metal-to-metal contact of the throttleplug and seat and around various piston rings arranged between the mainplug and the throttle plug. However, as should be understood, theleakage is primarily throttled across either the metal seat or thepiston rings and, to advantage, these components may be made fromerosion resistant, stainless steel.

As the valve continues to open, the main plug will continue to lift fromthe soft seat. Eventually, the retaining means will cause the throttleplug to move in tandem with the main plug to thereby displace thethrottle plug away from the second, metal seat. At this point, the fluidwill begin to flow freely through the valve and the primary fluidthrottling area will be across the second, metal seat. Inasmuch as thesecond, metal seat is spaced from the soft seat, the novel mainplug-throttle plug arrangement of the invention provides the advantagesof a soft seat valve shut off in a manner whereby the primary throttlingof the fluid flow is caused to occur at areas of the valve structurewhich are remote from the soft seat.

In accordance with another feature of the invention, the metal seat isarranged upstream from the soft seat and a fluid flow restrictor meansis arranged downstream from the soft seat. Accordingly, the fluid flowrestrictor means will serve as an additional principal throttling areato further reduce erosive fluid forces at the soft seat. Moreover, whenthe valve is in the fully opened position, all of the throttling will beacross the fluid flow restrictor means.

Thus, the present invention provides a control valve with the highlyadvantageous zero leakage shut off obtainable by utilizing a soft seatwhile, at the same time, greatly reducing the erosive effects of thefluid flow upon the soft seat by displacing the principal throttlingareas for the fluid flow away from the soft seat. The rim of the mainplug will, in each valve closing operation, fully conform thedeformable, resilient seat to its exact contour and configuration. Thethrottle plug will operate, in both valve opening and valve closingoperations, to provide a primary throttling area for the fluid flowcomprising an erosion resistant surface that is spaced from the softseat. The invention, therefore, teaches an effective and straightforward means for shielding the soft seat from harmful fluid floweffects within a valve structure arranged to shut off high pressurefluid flow by the exact mating between the main plug and the soft seat.

For a better understanding of the above and other features andadvantages of the invention, reference should be made to the followingdetailed description of a preferred embodiment of the invention and tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom plan view of the valve plug means of the presentinvention as shown within a fluid flow restrictor illustrated incross-section.

FIG. 2 is an exploded, perspective view of the valve plug means of thepresent invention.

FIG. 3 is a side cross-sectional view of a control valve according tothe present invention illustrating the valve in the fully closedposition and taken generally along line 3--3 of FIG. 1.

FIG. 4 is a side cross-sectional view of the control valve of FIG. 3illustrating the valve in the fully opened position and taken generallyalong line 4--4 of FIG. 1.

FIG. 5 is a partial side cross-sectional view of a modified version ofthe valve of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the drawings, and initially to FIG. 3, there isillustrated a high pressure control valve generally indicated by thereference numeral 10. The valve 10 comprises a valve body 11 including afluid inlet portion 12, an internal web portion 13 and a fluid outletportion 14 (see FIG. 4). A valve seat ring 15 is seated against agenerally annular recess 16 formed within the internal web portion 13 atthe area thereof adjacent the upper portions of the fluid inlet 12. Asclearly illustrated, the valve seat ring 15 is arranged to extend towithin the confines of the fluid inlet 12 and a trim gasket 17 isarranged between the annular recess 16 and the valve seat ring 15 toprovide a leak tight seal around the valve seat ring 15 therebypreventing fluid leakage from the fluid inlet 12 around the exterior ofthe valve seat ring 15 and into the internal web portion 13. The valveseat ring 15 is formed to include a partially tapered, partiallystraight walled fluid flow path 18 extending completely therethroughwhereby fluid is free to flow from the fluid inlet 12 through the flowpath 18 and toward the internal web portion 13. A fluid flow restrictormeans, in the form of a generally cylindrical valve cage 19, is providedwith a generally annular recess 20 formed at the lower end thereof. Therecess 20 is received over a section of reduced diameter 21 formed atthe upper end of the valve seat ring 15 whereby the cage trim 19 ismounted upon and in a coaxial relationship with the valve seat ring 15.

To advantage, the valve trim cage 19 includes a generally cylindricalflow path 22 extending axially through the cage 19 and generallyoverlying and forming a continuous flow path with the fluid passage 18of the valve seat ring 15. A series of radially extending flow paths 23are formed through the walls of the trim cage 19 and extend from theflow path 22 to the outer surface of the trim cage 19. The flow paths 23will act to subdivide any fluid flow through the flow path 22 into aplurality of substreams and, therefore, form a partial restriction tofluid flow. Accordingly, the trim cage 19 provides a primary throttlingarea for fluid flow, particularly when the valve 10 is in the fullyopened position, as will appear.

In order to secure the trim cage 19 in its mounted position upon thevalve seat ring 15, an upwardly extending rim 24, formed at the upperportion of the trim cage 15, is received within an annular recess 26provided near the lower end of the hollow interior of a hollowcylindrical cage spacer 25. The cage spacer 25 extends upwardly throughthe web portion 13 of the valve body 11 to a snug mating relation with avalve bonnet 27 which is secured to the valve body 11 in a well knownmanner (not specifically illustrated). A body-bonnet gasket 28 isarranged between the bonnet 27 and the valve body 11 and an upper trimgasket 29 is suitably secured between the bonnet 27 and the cage spacer25. The gaskets 28, 29 will prevent fluid leakage between the cagespacer 25, valve body 11 and the bonnet 27. The above-described mountingarrangement for the valve seat ring 15, trim cage 19, and cage spacer 25securely mounts these components within the web portion 13 of the valvebody 11 and between the annular recess 16 of the web portion 13 and thevalve bonnet 27. Moreover, a continuous, open fluid space is defined bythe fluid inlet 12, the flow path 18 of the valve seat ring 15, the flowpath 22 of the trim cage 19 and the hollow interior of the cage spacer25. Any fluid flow entering the valve body 11 through the inlet 12 willflow freely into the flow path 22 and out the several radial flow paths23 into the web portion 13. Thereafter, fluid flow will continue to thevalve outlet 14. The radial flow paths 23 of the trim cage 19 will actas a partial restriction to fluid flow, as discussed above, to therebythrottle and controllably disipate the kinetic energy of the highpressure flow through the valve body 11.

Pursuant to an important feature of the invention, the valve seat ring15 is arranged to define a "hard" valve seat and to provide a mountingfor a "soft" valve seat, which is spaced in the downstream directionfrom the "hard" seat. To that end, the diameter of the straight-walledportion of the flow path 18 is somewhat smaller than the diameter of theflow path 22 of the trim cage 19 to define an inwardly extending exposedsurface 30. The innermost edge 31 of the surface 30 is contiguous with adownwardly, inwardly tapered surface of finite length which defines avalve seat 32. To advantage, the valve seat ring 15 may be manufacturedfrom hardened stainless steel stock material whereby the valve seat 32will comprise a "hard" erosion resistant surface. Somewhat downstreamfrom the "hard" valve seat 32 is formed an annular,seat-insert-receiving recess 33. The width and position of the recess 33are such that the trim 19 partially overlies the recess 33.

In accordance with the invention, an annular insert 34 is received inthe recess 33 to define the "soft" seat. The seat insert 34 may be madefrom DuPont "Vespel", which is a high-temperature (500° F. to 900°)polymide plastic suitable for repeated compression and relaxation, asrequired in a soft valve seat design. As indicated above, the cage trim19 partially overlies the recess 33 to thereby retain the seat insert 34within the recess 33. In this manner, the valve seat ring 15 and trimcage 19 provide two, spaced valve seats 32, 34, each of which is exposedfor mating with a suitable valve plug to interrupt fluid flow throughthe valve body 11, as will be fully described below. The upstream valveseat 32 is made from hardened, erosion resistant stainless steel and istherefore suitable for forming a primary throttling area for the highpressure fluid flow, particularly during the time immediately beforeeither initial valve opening or valve closing. The downstream valve seat34 comprises a deformable, resilient material and will thereforeaccommodate a fully conformed mating between the seat 34 and acomplementary valve plug to provide a zero-leakage shut off.

Pursuant to another important feature of the invention, a novel valveplug means 35 is slideably received within the open space formed by theflow passage 22 of the trim cage 19 and the hollow interior of the cagespacer 25. The valve plug means 35 comprises a main valve plug 36 and aninner, auxiliary throttle plug 37. The valve-bonnet 27 is provided witha central opening 38 through which a valve stem 39 is received. The mainvalve plug 36 includes an upwardly extending projection 40 which isreceived within an opening 41 formed at the lowermost portion of thevalve stem 39 and secured therein by means of a pin 42. The valve stem39 is associated with a conventional valve actuator in a well knownmanner (not specifically illustrated) whereby the valve stem 39 may beselectively, axially displaced to thereby controllably lift and lowerthe main valve plug 36 through a predetermined valve stroke to open andclose the valve 10. The main valve plug 36 is formed to include a lowerholow portion 43 to slideably receive the throttle plug 37. The throttleplug 37 is axially displaceable relative to the main valve plug 36,within the hollow portion 43, through a predetermined limited distance.A metal piston ring 57 is secured about the throttle plug 37 to minimizefluid leakage between the throttle plug 37 and the main plug 36. Theportion of the main valve plug 36 circumscribing the lowermost end ofthe hollow, internal portion 43 is provided with a downwardly extending,circumferential rib element 44 which is vertically aligned with the softseat-insert 34. Accordingly, when the valve stem 39 is operated to lowerthe main valve plug 36 to its lowermost position, as illustrated in FIG.3, the rib portion 44 will be pressed against the deformable, resilientseat insert 34 to form a fully conformed leak-tight seal therebetween.Moreover, when the main valve plug 36 is in the above described closedposition, the main valve plug 36 will completely block off the radialfluid flow paths 23 of the trim cage 19 to interrupt fluid flow throughthe valve body 11. A U-shaped cup seal 45 is mounted within the recess26 to prevent fluid leakage between the main plug 36, cage spacer 25 andtrim cage 19.

To advantage, a series of flow openings 46, 47 is formed through each ofthe main plug 36 and throttle plug 37, respectively to allow fluid toflow above the valve plug means 35 and into the hollow interior of thecage spacer 25 (see FIGS. 1, 4). In this manner, the pressure effectsabove and below the valve plug 35 will tend to substantially balanceeach other out to reduce the stem forces necessary to move the valveplug 35. Moreover, due to the somewhat smaller diameter of the passage18 relative to the flow path 22, the fluid pressures acting upon thevalve plug 35 will be slightly unbalanced in the downward directionthereby tending to urge the valve plug 35 toward the closed valveposition.

An additional series of threaded openings 48 is formed through the mainplug 36 (see FIG. 3). The threaded openings 48 are each axially alignedwith a complementary opening 49 formed through the throttle plug 37. Aseries of bolts 50 are each received through one of the openings 49 andare threadedly engaged within the threaded opening 48 aligned with theparticular opening 49 to provide a means for retaining the throttle plug37 within the hollow portion 43 of the main plug 36. The bolts 50 eachextend well beyond the rim 44 and include an end portion of enlargeddiameter 51. More specifically, each end portion 51 has a diameter whichis somewhat larger than the internal diameter of the complementarythrottle plug opening 49 such that the throttle plug 37 will bottomagainst the end portions 51, as will appear. Moreover, a centrallydisposed, downwardly extending hub element 52 is formed within thehollow portion 43 of the main plug 36 to form an upper stop for thethrottle plug 37. In this manner, the throttle plug 37 is axiallymovable, relative to the main plug, between the hub element 52 and theend portions 51 of the bolts 50.

Pursuant to the invention, the distance between the hub portion 52 andthe bolt end portions 51 is arranged to be greater than the length ofthe throttle plug 37 and these elements are fixed relative to oneanother whereby the throttle plug 37 protrudes from the hollow portion43 for all axial positions of the throttle plug 37 between the hub 53and the bolt end portions 51, as clearly illustrated in FIGS. 3 and 4.The lowermost, protruding end of the throttle plug 37 is formed to aninwardly tapered, valve seat engaging surface 53 which is aligned andmatable with the hard valve seat 32. As should be understood, theprotruding valve seat engaging surface 53 and the rib portion 44 providethe valve plug means for engaging the above-described, spaced hard valveseat 32 and soft valve seat 34. The spatial relation between the seatengaging elements 53, 44 and the seats 32, 34, as well as the relativemovement permitted between the main and throttle plugs 36, 37 is suchthat the rib 44--soft seat 34 engagement will occur after the surface53--valve seat 32 engagement in a valve closing operation anddisengagement will occur before surface 53--valve seat 32 disengagementin a valve opening operation. As will be described more fully in thefollowing description of the operation of the valve, the sequence ofseat engagement and disengagement brought about by the mainplug-throttle plug and spaced hard seat-soft seat arrangement of theinvention will act to displace the primary throttling area for the fluidflow during valve opening and closing operations away from the softvalve seat insert 34.

In order to facilitate a near leak-tight seal between the surface 53 andthe hard valve seat 32 during valve closing and opening operations, aset of coil springs 54 is arranged between the main plug 36 and throttleplug 37. Each spring 54 is coaxial with one of the bolts 50 and actsbetween a first recess 55 formed within the hollow portion 43 of themain plug 36 and a second recess 56 formed in the upper portion of thethrottle plug 37. The springs 54 will tend to urge the throttle plug 37away from the hub 52 and in a valve seat engaging direction.

Referring now to FIG. 3, when the valve plug 35 is in the closedposition, the closing force developed by the valve stem 39 will betransmitted directly through the main valve plug 36 to the rib 44 toform the fully conformed, leak-tight seal between the rib 44 and thesoft seat insert 34, as discussed above. Moreover, the valve seatengaging surface 53 of the throttle plug 37 will be in a mating relationwith the hard seat surface 32. The central hub 52 is arranged to contactthe throttle plug 37 when the valve plug 35 is in the closed positionwhereby the forces developed by the valve stem 39 will also betransmitted through the main valve plug 36, hub 52, and throttle plug 37to the hard valve seat 32 to form a near leak-tight seal between thesurface 53 and hard valve seat 32. When the valve is to be opened, thevalve stem 39 will be moved upwardly to thereby lift the main valve plug36 and displace the rib 44 from the soft seat insert 34. During theupward movement of the main valve plug 36, both the springs 54 and theslightly unbalanced pressure effects discussed above will tend tomaintain the throttle plug 37 in contact with the hard valve seat 32. Atthis time, the only fluid flow will be a minimal amount of leakagebetween the surface 53 and hard valve seat 32 and around the metalpiston ring 57. It should be understood that all of such fluid leakagewill be primarily throttled across the hard, erosion resistant metalseat 32 and metal piston ring 57.

Upon continued upward movement of the main valve plug 36, the throttleplug 37 remains in contact with the hard valve seat 32 until thethrottle plug 37 bottoms against the portions 51 of the bolts 50. In thepreferred embodiment, the plug 37 bottoms against the portions 51 whenthe main plug has exposed approximately 50% of the paths 23. Thereafter,further continued upward movement of the main valve plug 36 will causethe bolts 50 to lift the throttle plug 37 away from the hard metal seat32. At this point, the rib 44 will have been displaced a significantdistance from the soft seat insert 34 and the tapered surface 53 will bespaced a minimal distance from the hard valve seat 32 whereby fluid flowmay begin to flow from the flow path 18 into the fluid path 22 andthrough the radial flow paths 23. In such an arrangement, the initialfluid flow will be throttled primarily across the hard, erosionresistant metal seat 32 and thereafter further throttled by the radialflow paths 23 of the trim cage 19. Thus, there will be a minimal amountof erosive fluid forces acting upon the soft valve seat insert 34 whichis, at this point, spaced a significant distance from the rib 44,relative to the spacing between the surface 53 and the hard metal seat32 and, therefore, does not define a principal throttling area for fluidflow particularly in view of the primary throttling area formed betweenthe surface 53 and hard metal seat 32. Further continued upward movementof the main valve plug 36 will act to progressively expose more and moreof each of the radial flow paths to fluid flow until the paths 23 arefully exposed to fluid flow. At this time, the radial flow paths 23 willform the primary throttling areas for the high pressure fluid flowthrough the valve body 11.

During a valve closing operation, the valve stem 39 will lower the valveplug 35 whereby the main valve plug 36 will begin to close the radialflow paths 23 to fluid flow and the surface 53 approaches and eventuallycontacts the hard metal valve seat 32. As the surface 53 approaches thehard metal valve seat 32, the fluid flow will again be primarilythrottled in the increasingly smaller and smaller space between thesurface 53 and hard valve seat 32. At the point where the surface 53contacts the hard metal seat 32 to substantially close off fluid flowthrough the valve, the rib 44 will still be spaced a significantdistance from the soft seat insert 34, as in the corresponding positionof the valve plug 35 during a valve opening operation, and, therefore,will again not define a significant throttling area for the fluid flowrelative to the throttling area defined by the surface 53 and hard vavleseat 32. Once again, the fluid flow is substantially interrupted by themating engagement between the surface 53 and hard valve seat 53. At thistime, there will be a minimal amount of fluid leakage, throttledprimarily over the hard valve seat 32 and metal piston ring 57. To fullyclose the valve, the valve stem 39 will move further downward tocontinue to lower the main valve plug 36 until the rib 44 engages thesoft seat insert 34. During this time, the throttle plug will moverelative to the main valve plug 36 within the hollow portion 43 untilthe throttle plug 37 once again engages the hub 52 whereupon furtheradditional forces developed through the valve stem 39 will once againact to form a fully conformed, zero-leakage seal between the rib 44 andthe soft seat insert 34 and a near zero-leakage seal between the surface53 and hard metal seal 32.

Thus, the present invention provides a highly effective valve structureoperable to provide a complete isolation of high pressure fluid from thevalve outlet when the valve is in the closed position and to achieve afluid flow through the valve body in a manner whereby there is a minimalamount of erosive effects by the high pressure fluid flow in the area ofthe soft valve seat. The highly advantageous valve operation is achievedthrough a unique arrangement of a double hard seat-soft seat as well asa double main valve plug, throttle plug configuration wherein thegeometry between these components and a relative motion permittedbetween the main plug and throttle plug provide valve opening andclosing operations which tend to isolate the deleterious effects of thefluid flow to hard, erosion resistant surfaces which are remote from thesoft seat forming portion of the valve structure. Accordingly, the valveof the present invention may be operated through repeated valve openingand valve closing operations while forming a zero-leakage valve shut offat each valve closing and while operating in a manner to greatly extendthe worklife of the material forming the soft valve seat.

FIG. 5 is a partial cross-sectional view of a modified version of thevalve of FIG. 3. As illustrated, the main valve plug 36' includes aportion of increased diameter 236 arranged to be slideably receivedwithin a generally cylindrical recess 225 formed within the hollowinterior of the spacer 25'. A series of fluid flow paths 250 are formedthrough the portion of increased diameter 236 of the main valve plug36'. In addition, the diameter of the main valve plug 36' above theportion 236 is substantially equal to the diameter of the throttle plug37'. The modified structure of the valve plug 36', as illustrated inFIG. 5, as well as the additional fluid flow paths 250, provide a highlyadvantageous balancing means whereby the valve plug 35' may be axiallydisplaced by the valve stem 39' in a smooth valve opening and valveclosing operation. More specifically, when the valve is in the closedposition, the inlet fluid pressure which leaks passed the piston ring57' or the valve seat 32' will leak through the flow path 250 to theportions of the cylindrical recess 225 above the portion 236 of the mainvalve plug 36'. In addition, the high inlet pressure fluid may also flowthrough a series of openings similar to the openings 46, 47 of the valveof FIG. 3 to above the valve plug 35'. In this manner, the valve plug35' will be substantially balanced when in the closed position. During avalve opening operation, the main plug 36' will lift from the soft valveseat 34' and the fluid pressure acting both above and below the portion236 will decrease to the outlet pressure. However, the inlet pressureacting upon the valve plug 35' will remain substantially balancedinasmuch as the upper diameter of the main valve plug 36' issubstantially equal to the diameter of the throttle plug 37' exposed tohigh pressure inlet fluid. The above described configuration for themain valve plug 36' eliminates any possible unbalanced pressurereversals which may occur due to changes in the exposure of each of themain valve plug 36 and throttle plug 37 (see FIG. 3) to high pressureinlet fluid during a valve opening and valve closing operation. In allother respects, the valve of FIG. 5 is identical to the valve of FIG. 3.

In order to prevent fluid leakage from the hollow interior of the cagespacer 25' and around the upper portion of the main valve plug 36', agenerally annular cap member 251 is threadedly secured to the upperportion of the main valve plug 36' by the bolts 50' and mount a U-cupsealing member 252 in a sealing relation between the hollow interior ofthe cage spacer 25' exposed to high pressure fluid and the outer surfaceof the upper portion of the main valve plug 36'. Moreover, to advantage,the fluid flow restrictor 253 comprises a restrictor of the typedisclosed in U.S. Pat. No. 4,249,574, the disclosure of which isexpressly incorporated herein by reference.

The above-described preferred embodiments of the invention are meant tobe representative only as certain changes may be made therein by personsskilled in the art without departing from the clear teachings of theinvention. Accordingly, reference should be made to the followingappended claims in determining the full scope of the invention.

We claim:
 1. A high pressure fluid control valve which comprises(a) avalve body including an internal flow path defining a fluid inlet and afluid outlet, (b) a first valve seat arranged within said internal flowpath, (c) a second valve seat arranged within said internal flow path ina spaced relation to said first valve seat, (d) a main valve plugcomprising integral upper and lower portions, (e) said main valve plugbeing selectively, axially movable within said internal flow path andmatable with said first valve seat to interrupt fluid flow between thefluid inlet and the fluid outlet, and (f) a throttle plug axiallymovable within said internal flow path in a predetermined relativemotion with respect to said main valve plug, and matable with saidsecond valve seat to interrupt fluid flow between the fluid inlet andthe fluid outlet, (g) at least the lower portion of said main valve plugincluding a bore formed therein, (h) said throttle plug being receivedin said bore whereby said throttle plug is in a coaxial, telescopingrelation with said main valve plug, (i) said throttle plug being movablerelative to said main valve plug within said bore through saidpredetermined limited distance, whereby during a valve opening operationsaid main valve plug lifts from said first valve seat before saidthrottle plug lifts from said second valve seat, thereby throttlinginitial fluid flow primarily across said second valve seat, (j) saidlower portion of the main valve plug having an outer diameter that isgreater than the outer diameter of said upper portion of the main valveplug, (k) the outer diameter of the upper portion of said main valveplug being substantially equal to the outer diameter of said throttleplug, (l) at least one fluid flow path being formed completely throughsaid lower portion of the main valve plug whereby fluid may flow frombelow to above said lower portion of the main valve plug, (m) at leastone flow path being formed completely through the throttle plug and theupper portion of said main valve plug whereby fluid may flow from belowthe throttle plug to above the upper portion of the main valve plug, (n)the portions of said internal flow path above the upper portion of themain valve plug being isolated from the portions of said internal flowpath which overlie the larger outer diameter lower portion of the valveplug, (o) whereby fluid leakage across the main valve plug and throughthe flow path formed through the lower portion of the valve plug willflow to a portion of the internal flow path of the valve body which isisolated from the portions of the internal flow path above the upperportion of the main valve plug, thereby eliminating any unbalancedpressure reversals which may occur due to changes in the exposure ofeach of the main valve plug and throttle plug to high pressure inletfluid during a valve opening operation.
 2. The high pressure fluidcontrol valve according to claim 1, further characterized by(a) saidfirst valve seat comprising a deformable resilient material, and (b)said second valve seat comprising a hardened erosion-resistant material.